The present invention relates generally to the field of subterranean exploration and drilling and, more particularly, to a method and system for accessing subterranean zones from a limited surface area.
Subterranean deposits of coal, whether of xe2x80x9chardxe2x80x9d coal such as anthracite or xe2x80x9csoftxe2x80x9d coal such as lignite or bituminous coal, contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal deposits has occurred for many years. Substantial obstacles have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas, up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.
Horizontal drilling patterns have been tried in order to extend the amount of coal seam exposed to a drill bore for gas extraction. Traditional horizontal drilling techniques, however, require the use of a radiused well bore which presents difficulties in removing the entrained water from the coal seam. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores.
Prior mining systems also generally require a fairly large and level surface area from which to work. As a result, prior mining systems and drilling technologies generally cannot be used in Appalachia or other hilly terrains. For example, in some areas the largest area of flat land may be a wide roadway. Thus, less effective methods must be used, leading to production delays that add to the expense associated with degasifying a coal seam.
The present invention provides a method and system for accessing subterranean zones from a limited surface area that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, from a common bore an articulated well bore with a well bore pattern in a subterranean seam extends from or proximate to a cavity well in communication with the well bore pattern in the seam. The well bore patterns provide access to a large subterranean area while the cavity well allows entrained water, hydrocarbons, and other deposits collected by the well bore pattern to be efficiently removed and/or produced. The well bore pattern also provides access to the subterranean zone for treating material within the subterranean zone or introducing or injecting a substance into the subterranean zone.
In accordance with one embodiment of the present invention, a system for extracting resources from a subsurface formation includes a substantially vertical well bore extending from the surface to a target zone. The system also includes an articulated well bore extending from the substantially vertical well bore to the target zone. The articulated well bore diverges from the substantially vertical well bore between the surface and the target zone. The system also includes a drainage pattern extending from the articulated well bore in the target zone and operable to collect resources from the target zone. The system further includes a subsurface channel operable to communicate resources from the drainage pattern to the substantially vertical well bore. The system also includes a vertical pump disposed in the substantially vertical well bore and operable to lift resources collected in the substantially vertical well bore to the surface.
In accordance with another aspect of the present invention, the substantially horizontal drainage pattern may comprise a pinnate pattern including a substantially horizontal diagonal well bore extending from the substantially vertical well bore that defines a first end of an area covered by the drainage pattern to a distant end of the area. A first set of substantially horizontal lateral well bores extend in a spaced apart relationship relative to each other from the diagonal well bore to the periphery of the area on a first side of the diagonal well bore. A second set of substantially horizontal lateral well bores extend in a spaced apart relationship relative to each other from the diagonal well bore to the periphery of the area on a side of the diagonal opposite the first set. One or more of the substantially horizontal lateral well bores may further comprise a curved or radiused portion proximate to the diagonal well bore.
Technical advantages of the present invention include providing an improved method and system for accessing subterranean deposits from a limited area on the surface. In particular, a well bore pattern is drilled in a target zone from an articulated surface well at least in close proximity to a cavity well. The well bore pattern is interconnected to the cavity well by a channel through which entrained water, hydrocarbons, and other fluids may be drained from the target zone and efficiently removed and/or produced by a rod pumping unit. As a result, gas, oil, and other fluids from a large, low pressure or low porosity formation can be efficiently produced at a limited area on the surface. Thus, gas may be recovered from formations underlying rough topology. In addition, environmental impact is minimized as the area to be cleared and used is minimized.
Another technical advantage of the present invention includes providing an improved well bore pattern for accessing an increased area of a subterranean zone. In particular, a pinnate well bore structure with a main well bore and opposed laterals is used to maximize access to a subterranean zone from a single well bore. Length of the laterals is maximized proximate to an articulated well bore used to form the well bore pattern and decreases toward the end of the main well bore to provide uniform access to a quadrilateral or other grid area. The first set of laterals proximate to the articulated well bore may comprise a curved or radiused portion proximate to the main well bore, allowing greater spacing between the laterals and, therefore, greater coverage of the subterranean zone. This allows the well bore pattern to be aligned with longwall panels and other subsurface structures for more efficient degasification of a mine coal seam or other deposit.
Yet another technical advantage of the present invention includes providing an improved method and system for preparing a coal seam or other subterranean deposit for mining and for collecting gas from the seam after mining operations. In particular, a surface well, with a vertical portion, an articulated portion, and a cavity, is used to degasify a coal seam prior to mining operations. This reduces both needed surface area and underground equipment and activities. This also reduces the time needed to degasify the seam, which minimizes shutdowns due to high gas content. In addition, water and additives may be pumped into the degasified coal seam through the combined well prior to mining operations to minimize dust and other hazardous conditions, to improve efficiency of the mining process, and to improve the quality of the coal product. After mining, the combined well is used to collect gob gas. As a result, costs associated with the collection of gob gas are minimized to facilitate or make feasible the collection of gob gas from previously mined seams.
Still another technical advantage of the present invention includes an improved method and system for accessing multiple subterranean deposits from a limited area on the surface. In particular, a first well bore pattern is drilled in a first target zone from a first articulated surface well in close proximity to a cavity well bore. The first well bore pattern is interconnected to the first cavity well bore by a first channel. A second well bore pattern is drilled in a second target zone from a second articulated surface well in close proximity to the cavity well. The second well bore pattern is interconnected to the cavity well by a second channel. As a result, multiple subterranean formations may be accessed from a limited area on the surface. For example, gas may be recovered from multiple formations underlying rough topology. In addition, environmental impact is minimized as the area to be cleared and used is minimized. Furthermore, overall drilling time is minimized as multiple drainage patterns are drilled while the drilling equipment is still on site, eliminating the need to take down and set up the drilling equipment more than once.
In another embodiment of the present invention, an articulated well bore and cavity well bore each extend from a surface location generally within 100 feet or less of each other, minimizing the surface area needed for production and drilling equipment. In one embodiment, the articulated well bore and the cavity well bore comprise a common portion at or near the surface. A well casing extends from the surface to the end of the common portion distal to the surface. As a result, the cavity and articulated well bores can be formed from a roadway, steep hillside, or other limited surface area. When the articulated and cavity well bores comprise a common portion, all drilling equipment may be located within a 100 square foot area on the surface. Accordingly, environmental impact is minimized as less surface area must be cleared.
Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims.